Technical Field
The present disclosure relates to imaging apparatuses equipped in such as digital cameras or portable phones.
Description of the Related Art
Various methods have been proposed for measuring a depth of three-dimensional scene in noncontact manner, to be more specific, for measuring a distance to an object to be captured. These methods are divided broadly into two categories, namely, an active method and a passive method. The active method irradiates the object with an infrared ray; an ultrasonic wave, or a laser beam, and then measures a time until a reflective wave returns, or measures an angle of the reflective wave, thereby calculating the distance. The passive method calculates the distance based on an image of the object. The passive method is widely used in cameras because the passive method does not need a device for irradiation of the infrared ray.
A method of DFD (Depth from Defocus, and this method is referred to simply as DFD hereinafter) is disclosed as one of the passive methods. DFD calculates the distance based on blur information which shows changes in size or in shape depending on the distance to the object. DFD does not need multiple cameras, and allows measuring the distance based on a small number of images. A process of measuring a distance to an object by using DFD is referred to as a DFD process.
A principle of DFD is briefly described hereinafter. DFD is a method for measuring a distance based on blur information obtained from multiple images having different in-focus positions. A captured image containing a blur is formed by convoluting a point spread function (PSF), which is a function of a distance to an object, onto an omni-focal image that shows no blur caused by lenses. Since PSF uses the distance to the object as a vas DFD detects the blur from the blurred image, thereby finding the distance to the object.
At this time, one formula is established among a blurred image, omni-focal image, and a distance to an object, with respect to a blurred image of which omni-focal image and a distance to the object stay as unknowns. Imaging another blurred image having an in-focus position different from the present blurred image will create another formula, and solving these multiple formulae allows finding the distance to the object. Patent Literature 1 and other documents disclose how to obtain and solve the formulae.